Cutaneous markers of internal malignancy. I. Malignant involvement of the skin and the genodermatoses.

Cutaneous findings often reflect the presence and course of an internal disease. Recognition of external clues is important to facilitate both early diagnosis and prompt treatment of the internal disorder. Early recognition is especially valuable in a patient with an internal malignant disease because intervention may significantly affect survival. In this two-part series, we review the spectrum of cutaneous markers of internal malignancy. Part I focuses on malignant involvement of the skin caused by either direct extension or metastases and the genodermatoses with malignant potential. Part II will be devoted to the paraneoplastic skin manifestations of internal malignancy as well as environmental carcinogens that produce cutaneous features. We also discuss some proposed but controversial associations between skin disease and internal malignancy.